Effects Of Compost Containing Cadmium And Ciprofloxacin On Antibiotic Resistance Genes And Microbial Community In Lettuce

With the development of modern livestock industry,feed demand increased year by year.Therefore,the content of heavy metals and antibiotics added to the feed also increased,and lead to a large number of heavy metals,antibiotics excreted with livestock and poultry.Livestock manure is applied to soil as organic fertilizer,and the antibiotics and heavy metals of feces could affect soil environment and crop quality.Therefore,this experiment selected ciprofloxacin(CIP),a kind of antibiotic used in both human and animals,and cadmium(Cd),to study the effects of organic fertilizer combined with cadmium and different concentrations of ciprofloxacin on yield and quality of lettuce,antibiotic resistance genes(ARGs),the soil microbial community structure and the endophytic bacteria in lettuce leaves by pot experiment.The main results are as follows:(1)Lettuce yield was improved by applying organic fertilizer containing Cd and CIP.Low concentration of CIP increased the leaf yield,chlorophyll and vitamin C content,and high levels of CIP showed a certain inhibitory effect.The combination of Cd and low concentration CIP played the most important role in promoting lettuce yield.High levels of CIP promoted the absorption of Cd at the root of lettuce,and decreased the accumulation of Cd in leaves.(2)The application of organic fertilizer containing Cd and CIP increased the relative abundances of ARGs in soil to different extent,and significantly increased the abundance of int1 in leaves.In soil,ARGs increased with the increase of CIP concentration,and the increase of qnrA,qnrS,qnr D,int1 and int2 in Cd and CIP composite treatments was greater.The relative abundances of 4 kinds of ARGs in leaves increased with the increase of CIP concentration.(3)The application of organic manure containing Cd and CIP to some extent affected the soil microbial community structure and endophytic bacteria in lettuce leaves.Organic fertilizer containing CIP increased soil microbial community diversity,decreased the richness of microbial community,and inhibited the diversity and abundance of endophytic bacteria in leaves.The combined pollution of Cd and low concentration of CIP inhibited the diversity and abundance of soil microorganisms and leaf endophytes.The abundances of bacteria such as Fluviicola,Candidatus,Nitrososphaera and Kaistobacter increased with the increase of CIP concentration.The application of organic fertilizer containing Cd and CIP increased the abundances of Streptococcus,Prevotella,[Prevotella] and Neisseria in lettuce leaves.Treponema,Fusobacterium and Leptotrichia spp.were increased with the increase of CIP concentration.The utilization of organic manures containing Cd and CIP increased the abundance of potential pathogenic bacteria such as Streptococcus,Prevotella and Porphyromonas in leaves.These pathogenic bacteria may transfer to human body along the food chain and threaten human health.To sum up,the application of organic fertilizer containing Cd and CIP,high concentration CIP have inhibitory effect on the yield of lettuce;Cd and CIP increased ARGs abundance in soil and leaf lettuce;Containing Cd and CIP organic fertilizer affected soil and lettuce leaves endophytic microbial community diversity and richness,induced by antibiotic resistant bacteria genus of pathogenic bacteria and increase.